Synchronous motor



y 14, 1936- M. E. THOMPSON SYNCHRONOUS MOTOR Filed Sept. 11, 1955 2 Sheets-Sheet l lNVENTOR M 1 ton E. Thompson BY fill/CM, gm legit 7/ M ATTORNEYS July 14, 1936. THOMPSON 2,047,528

SYNCHRONOUS MOTOR Filed Sept. 11, 1935 2 Sheets-Sheet 2 INVENTOR Mz lion E. Thompson BY 73%, 8 /11 ,Jwfif/M ATTORNEYS Patented July 14, 1936 UNITED STATES PATENT OFFICE SYNCHRONOUS MOTOR Milton E. Thompson, Ridg'way, Pa. Application September 11, 1935, Serial No. 40,109

7 Claims.

The present invention relates to small synchronous motors for clocks or the like and comprises a single-input bi-polar motor of novel construction which operates eiiiciently and quietly on a fraction of the power input required by motors now on the market. The new motor may be constructed to run at relatively low speeds, does not overheat and has uni-directional rotation.

The particular motor illustrated in the accompanying drawings and hereinafter more particularly described is not self starting but certain of the novel features of the invention are applicable to self starting as well as to non self starting motors as will be apparent to those skilled in the art.

For an understanding of the invention reference may be had to the accompanying drawings of which:

Fig. 1 is a face view of a motor constructed acand representing the.

structure suitable for use with the rotor of Fig.

1; and

Fig. 5 is a face view of the pole faces and rotor of a motor constructed according to the invention and representing another embodiment thereof.

The field of the motor illustrated in Figs. 1 to 3 inclusive comprises a single field coil 2, a laminated core 4 and laminated pole pieces 6 and 8. Coil 2 is of a relatively large number of turns of fine enameled copper wire. Each pole piece, in the preferred embodiment of the invention illustrated, is built up of fifteen laminations of sheet steel and each piece is provided with a deep slot 9, perpendicular to the axis of rotation of the rotor, dividing the pole piece into front and rear sections of substantially equal thickness. Each slot 9 receives a shading band 10 of solid copper which completely encircles the front section of the pole piece. vided with spaced teeth I2 along the periphery of the arc'uate portions facing the rotor. In the particular embodiment of the invention illustrated the tooth pitch is twelve degrees as meas ured from the rotor axis and the teeth It on one section of a pole face are in alinement with the teeth on the other section of that pole face.

The rotor comprises a central hub portion l4 mounted on a shaft I6 and carrying two disks ll and I 8 each of which is approximately of the Each section of each pole piece is prothickness of one pole section and which are separated by a distance equal to the width of slots. 9. Disk I1 is provided with aplurality of teeth l9 of the same pitch as teeth [2 and disk I8 is provided with similar teeth 20. The teeth 20 on 5 disk l8 are advanced relatively to the teeth It! on disk i1 through an angle between one fourth and one half of a tooth'pitch. The circumferential width of the faces of each of teeth l2, l9 and 20 is five degrees. In the motor of Figs. 1 to 3, 10

' each pole section is provided with fourteen teeth and each rotor disk with thirty teeth.

' Withthe above described construction, when sixty cycle alternating electro-motive force is r applied across the terminal 22 of the field c011 and the rotor is given an initial rotation, counterclockwise as viewed in Fig. 1, the torque created by the rotating field will quickly speed up the rotor until it is rotating in synchronism with thefield. At synchronism each tooth H of the shaded pole sections of the field exerts a considerable forward pulling torque on teeth IQ of disk I! and each tooth l2 of the unshaded pole sections exertsa similar forward pulling torque on teeth 20 of disk I8. The torque between cooperating 25 field and rotor teeth varies with the relative position of the teeth and drops to zero when the teeth are in alinement. As any rotor tooth can only pass forward beyond the field tooth with which it has just been alined during the period of reversal of magnetization of the field tooth and as such reversal occurs twice during each alternating current cycle, it follows that but two rotor teeth can pass any one field tooth during one complete cycle. Therefore, at synchronism,

if each rotor disk has thirty teeth, as in the embodiment illustrated, the rotor will make one complete rotation every fifteen cycles of magnetization' and-the .motor when operated on sixty cycle alternating current will run at 240 R. P. M. 40 The teeth of the shaded front section of each pole exert maximum forward torque upon rotor teeth is at the moment when a slight negative or backward torque is exerted upon rotor teeth 20 by the teeth of the unshaded sections and vice versa. Thus because of the novel rotor and field constructions there is an overlapping of positive and negative torque which produced a resultant torque on the rotor as a whole and this resultant torque never reverses and is, in fact, fairly constant at all times. This nearly constant forward torque gives a high degree of stability to the motor and prevents hunting even under severe voltage changes.

In the preferred embodiment of the invention.

been illustrated and as above indicated, each pole piece section has fourteen teeth, each rotor disk has thirty teeth and the speed of the motor is 240 R. P. M. Without substantially impairing the operation of the motor, various changes could be made in the number and distribution of the polar and rotor teeth. For example, a satisfactory field structure, for use with the rotor of Figs. 1 to 3, is that illustrated in Fig. 4 wherein the pole faces to and 8a are split into shaded and unshaded sections as in the embodiment illustrated in Figs. 1 to 3 by slots perpendicular to the axis of rotation of the motor and but eight teeth 12a of the same pitch as those of the rotor are provided on each pole face section. A motor having the field structure of Fig. 4 and the rotor of Figs. 1 to 3 will operate substantially as described in connection with the preferred embodiment of the invention and at the same speed, namely 240 R. 1?. M. As compared with the field structure of the motor of Fig. 1, the arrangement of Fig. 4 corresponds to the suppression of the first and last three polar teeth of each pole piece section.

The embodiment of theinvention illustrated in Fig. 5 is an example of another possible field structure in which each pole piece section has but eight teeth. As compared with the field structure of the motor of Fig. l the arrangement of Fig. 5 corresponds to second, fourth, sixth, ninth, eleventh and thirteenth teeth, counting from the bottom, of each pole piece section. Thus each pole piece section has the teeth M1) on its upper half staggered relatively to the teeth We on the lower half of that section while the tooth pitch of each half of each section is twice that of the teeth of the pole piece sections of the motor of Fig. l or of that of Fig. 4. With the field structure of Fig. 5, the rotor of Figs. 1 to 3, without change, or a rotor such as illustrated at M, in which each disk has but fifteen teeth could be used. In either case the motor speed will still be 240 R. P. M. Rotor 24, like the rotor of Figs. 1 to 3 comprises two toothed disks of which the teeth on the disk cooperating with the mishaped pole pieces are advanced anywhere from three to six degrees as measured from the axis of rotation of the rotor. structurally rotor 2d corresponds to the rotor of Fig. i with alternate teeth removed from each dish.

, Various embodiments of the invention have now described in each oi which the field structure includes a pair oi pole pieces slit perpendicularly to the axis 02 rotation of the motor, one section of each pole iace being shaded, and each section being provided with teeth. The rotor in each embodiment oi the invention illus trated and described includes a pair oi toothed disks, one cooperating with the shaded pole piece sections and the other cooperating with the unshaded pole piece sections. in each oi. the em bodirnents illustrated a fairly constant uni-dime tional torque is obtained because of the advance of the teeth on the rotor dish cooperating with the unshaded pole sections relative to the teeth on the other rotor dish and. because of the aline ment oi the teeth on the unshaded and shade pole piece sections. The same effect could be obtained with a rotor having alined teeth on its two disks, or having a single disk oi? sufficient width to cooperate with both pole piece sections, provided the teeth on the shaded pole piece sections were advanced reiatively to those on the the suppression of the unshaded pole piece sections. In either arrangement the magnetic pull of the teeth of the unshaded pole section upon the rotor teeth occurs prior to' the magnetic pull of the teeth of the shaded pole section upon the rotor teeth.

The following is claimed:

1. A single phase synchronous motor having a toothed rotor and a bi-polar field structure, including a single field coil and pole pieces having arcuate faces cooperating with pole piece being slit into two sections on a plane perpendicular to the axis of rotation of the rotor, a pair of shading bands one about one section of each pole piece, and cooperating teeth on said rotor and on pole sections, the teeth being so distributed that during any magnetic cycle the pull on the rotor teeth exerted by the teeth on an unshaded polar section precedes the pull on the rotor teeth exerted by the teeth on 2. A single coil bi-polar synchronous motor including a rotor and a pair of pole pieces divided into sections on a plane perpendicular to the axis of rotation of the rotor, a shading band on one section of one pole piece, a corresponding section of the other pole piece, said rotor comprising a pair of disks one positioned to rotate between the unshaded pole piece sections and the other positioned to rotate between the shaded pole piece sections, and cooperating teeth on said rotor disks and on said pole piece sections, the teeth on the shaded and unshaded sections of each pole piece being in alinement and the teeth on the rotor disk cooperating with the said rotor, each 10 the arcuate faces of said 15 the shaded polar section. 20

shading band on the 25 unshaded pole piece sections being advanced 35 relatively to those on the other rotor disk.

3. A motor according to claim 2 wherein the advance of the teeth on the one rotor disk relative to the teeth on the other rotor disk is between one fourth and one half of a tooth pitch.

4. A motor according to claim 2 wherein the teeth on the pole piece sections and on the rotor disks have the same pitch and are uniformly distributed along the cooperating surfaces of pole pieces and rotor.

5. A single phase synchronous motor having a rotor and a bi-polar field structure including a single field coil and laminated pole pieces having arcuate races cooperating with said. rotor, said rotor comprising a pair of disks each provided with uniformly spaced teeth about its periphery, the teeth oi? one disk being shifted circumferen tially relative to the teeth on the other disk, said pole pieces each being divided into sections by a slot extending perpendicular to the axis tion of the rotor, and each section being pro vided with alined teeth along the arcuate thereof for cooperating with the teeth of said rotor disks, and means for shading corresponri ing sections of each pole piece.

6. The motor according to claim 5 wherein the teeth on one halioi' each pole piece section are staggered relativeh. to the teeth on the other hair of the same pole piece section.

7. The motor according each pole piece section fourteen uniformly spaced teeth and rotor dish has thirty uni iormly spaced teeth and the teeth on the rotor disk cooperating with the unshaded poie piece h sections are advanced etween one fourth 1 one oi the tooth pitch.

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